1. Field of the Invention
The present invention relates to an automatic focus detecting apparatus for a lens interchangeable type camera and, more specifically, to an improvement of an automatic focus detecting apparatus employed for a single lens reflex camera.
2. Description of Related Art
Conventionally, in an automatic focus adjusting apparatus which detects a focus condition of a photographic lens to drive the lens to an in-focus position, the lens is sometimes initially set at an intermediate focusing position for every photographing operation in order to shorten the time required for driving the lens to the in-focus position after the focus detection (U.S. Pat. No. 4,265,528). However, in the prior art, the initial stop position of the lens was not determined to enhance the capability or the possibility of focus detection, so that the possibility of focus detection was low.
Meanwhile, in the automatic focus adjusting apparatus which detects the focus detection of the photographic lens to drive the lens to the in-focus position, if the focus detection is impossible, an operation of searching a lens position at which the focus detection is possible while driving the lens (the operation is called low contrast scanning) has been proposed (see Japanese Patent Laying-Open Gazette No. 182411/1984).
However, the low contrast scanning requires long period of time for the focus detection.